What are those strange noises on your airplane!?

 

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I guarantee most of you have experienced this, especially if you have done any air travel recently. You hear a strange noise as your plane leaves the gate before departure and again shortly after landing before pulling up to the arrival gate. A strange sawing or barking sound originating beneath your feet.

 Inevitably, while you’re worrying about the unsettling experience of your airplane marking strange noises, somebody within earshot, usually a child but not always, wonders out loud “what is that noise?” Well, I’m here to tell you so you can be THAT smarty pants on your next flight. I’d even go so far as to say this information will make you a hero to those already apprehensive about flying, and right off the bat I’ll say you have absolutely nothing to worry about. 

The noise is normal, and going further, will now become comforting. When you hear it, you’ll know for sure that all is well. This noise mostly pertains to Airbus aircraft, specifically the A320 family, but I can confirm it also occurs on the A319 since I was on one most recently. 

The sawing or barking sound you hear is from a hydraulic component called the PTU or Power Transfer Unit. It powers hydraulic systems, like flaps, landing gear, doors, or any manor of things requiring hydraulic force. If you’re wondering what hydraulics are, it’s what moves the giant bucket of a bulldozer or back hoe. It’s a bunch of hoses that force oil under pressure to actuate and move various articulating things…on an airplane, again, that would be stuff like the flaps, the rudder, the landing gear, etc.

You only usually hear the PTU making noise during taxi. When an Airbus A320 is moving around on the ground, usually only one of the engines is running to conserve fuel. When one of the engines is off, the PTU picks up the slack in powering some hydraulic systems. When in flight, obviously both engines are running and directly powering necessary hydraulic systems like the flaps, rudder, landing gear etc.

Speaking of landing gear, that solid clunk you hear and feel in your feet is the landing gear thunking up into the bay after take off and then thunking back down again a minute or so before landing. It is completely normal and again, hearing those thunks after take off and before landing is comforting. It means the landing gear is working normally.

Finally, on the subject of normal aircraft operation, let me ease some more fears as I think of them off the top of my head. 

First, those little wire barbs coming off the wings are static electricity discharges and also serve to divert lightning around the plane. As an airplane flies, it can build up static electricity. Those little barbs discharge the static electricity sparks into the air. 

Also, airplanes are designed to be struck by lightning. You have nothing to worry about. In fact, if the plane gets struck by lightning you’ll probably never notice. You’ve probably been on a plane while it gets struck. The bolt of lighting goes around the outside of the plane harmlessly on its way to the ground. Just about the worst you’ll encounter, possibly, are the cabin lights flickering or your entertainment screen spaz out for a second.

One more thing to ease your mind. No commercial airliner has ever been brought down by turbulence during level flight. There have been freak down bursts during take off and landing, but those have been almost insignificantly rare. What I’m talking about is the turbulence experienced at cruising altitude…but even at a few thousand feet above the ground it’s not serious. If you’ve been on a plane that violently drops in elevation or bounces around so hard you lose your lunch and plead with Jesus…I know it’s scary, but you’re going to be absolutely fine. The plane is structurally designed to handle more violence than you can dream of. In other words, imagine the worse turbulence you’ve ever encountered, multiply it by 100, and still the plane wouldn’t even begin to bat an eye. You’ll be horrified, but you’ll be perfectly safe other than possibly bumps and bruises if you’re not wearing your seat belt…so buckle up. So again, you’ll be uncomfortable but you’ll be 100% safe to complain about it to your friends and family when you land.

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